Measuring method, apparatus and substrate

Patent metadata

Field	Value
Publication number	US-10151987-B2
Application number	US-201113306668-A
Country	US
Kind code	B2
Filing date	Nov 29, 2011
Priority date	Nov 30, 2010
Publication date	Dec 11, 2018
Grant date	Dec 11, 2018

Abstract

A pattern formed on a substrate includes first and second sub-patterns positioned adjacent one another and having respective first and second periodicities. The pattern is observed to obtain a combined signal which includes a beat component having a third periodicity at a frequency lower than that of the first and second periodicities. A measurement of performance of the lithographic process is determined by reference to a phase of the beat component. Depending how the sub-patterns are formed, the performance parameter might be critical dimension (CD) or overlay, for example. For CD measurement, one of the sub-patterns may comprise marks each having of a portion sub-divided by product-like features. The measurement can be made using an existing alignment sensor of a lithographic apparatus. Sensitivity and accuracy of the measurement can be adjusted by selection of the first and second periodicities, and hence the third periodicity.

First claim

The invention claimed is:

1. A method of measuring a parameter of performance of a lithographic process, the method comprising:
(a) forming a pattern on a substrate using at least one lithographic step, the pattern including first and second sub-patterns positioned horizontally adjacent one another on the substrate in a direction parallel to a surface of the substrate and perpendicular to a scanning direction, and having respective first and second periodicities;
(b) making observations of the adjacent first and second sub-patterns by scanning, with a single scanning spot, at least a portion of each of the first and second sub-patterns to obtain a combined signal including a beat component having a third periodicity at a frequency lower than that of the first and second periodicities, the beat component generated by interference between signals produced by diffraction from the first and second sub-patterns; and
(c) calculating from said combined signal a measurement of performance of the lithographic process, the calculated measurement being determined at least partially by a phase of the beat component.

2. A method as claimed in claim 1 wherein said first and second sub-patterns are both formed in the same lithographic step, and wherein at least one of said sub-patterns is formed so as to have an apparent position, relative to the other sub-pattern, which is dependent on said performance parameter.

3. A method as claimed in claim 2 , wherein said performance parameter is the dimension of a certain feature type formed on said substrate in said lithographic step.

4. A method as claimed in claim 1 , wherein at least one of said sub-patterns comprises a periodic array of marks and wherein each of said marks has a solid portion and a subdivided portion, the apparent position of each mark when observed in step (b) being dependent on said performance parameter of the lithographic process.

5. A method as claimed in claim 1 , wherein said first and second sub-patterns are formed in separate lithographic steps.

6. A method as claimed in claim 5 , wherein said performance parameter is overlay.

7. A method as claimed in claim 1 , wherein in the step (b) observations of the first and second sub-patterns are combined optically and converted into an electronic signal that already includes the beat component.

8. A method as claimed in claim 7 , wherein said pattern is observed by scanning the pattern with a sensor to generate said electronic signal, such that said beat component appears during said scanning as a time varying component in said electronic signal.

9. A method as claimed in claim 1 , wherein in step (b) observations of the first and second patterns are made simultaneously and converted into first and second electronic signals which are then combined electronically to obtain said combined signal.

10. An apparatus for measuring a parameter of performance of a lithographic process, the apparatus comprising:
a sensor operable to observe a pattern on formed on a substrate using said lithographic process, the pattern including first and second sub-patterns positioned horizontally adjacent one another on the substrate in a direction parallel to a surface of the substrate and perpendicular to a scanning direction, and having respective first and second periodicities;
an arrangement for combining observations of the adjacent first and second sub-patterns by scanning, with a single scanning spot, at least a portion of each of the first and second sub-patterns to obtain a combined signal including a beat component having a third periodicity at a frequency lower than that of the first and second periodicities, the beat component generated by interference between signals produced by diffraction from the first and second sub-patterns; and
a processor for calculating from said combined signal a measurement of performance of the lithographic process, the calculated measurement being determined at least partially by a phase of the beat component.

11. An apparatus as claimed in claim 10 wherein in operation said observations of the first and second sub-patterns are combined optically before being converted into an electronic signal that already includes the beat component.

12. An apparatus as claimed in claim 11 wherein said sensor is arranged to make said observations by scanning the pattern to generate said electronic signal, such that said beat component appears during said scanning as a time varying component in said electronic signal.

13. An apparatus as claimed in claim 10 wherein in said combining arrangement is arranged to obtain observations of the first and second patterns in the form of first and second electronic signals and to combing the first and second electronic signals to obtain said combined signal.

14. A substrate whereon a mark has been formed by a lithographic process, the mark being adapted for use in measuring a parameter of performance of the lithographic process and comprising first and second sub-patterns positioned horizontally adjacent one another on the substrate within a region sized to allow a single scanning spot to simultaneously scan at least a portion of each of the first and second sub-patterns in a direction parallel to a surface of the substrate and perpendicular to a scanning direction, and having respective first and second periodicities, wherein said sub-patterns are formed such that an apparent position of one sub-pattern relative to the other sub-pattern is dependent on said performance parameter, and wherein said first and second periodicities are such as to generate a beat pattern having a third periodicity at a frequency lower than that of the first and second periodicities, the beat component generated by interference between signals produced by diffraction from the first and second sub-patterns, whereby variation of said performance parameter can be inferred a variation in the position of the beat pattern.

15. A substrate as claimed in claim 14 wherein said first and second sub-patterns are both formed in the same lithographic step, and wherein at least one of said sub-patterns is formed so as to have an apparent position, relative to the other sub-pattern, which is dependent on said performance parameter.

16. A substrate as claimed in claim 15 wherein said performance parameter is the dimension of a certain feature type formed on said substrate in said lithographic process.

17. A substrate as claimed in claim 14 , wherein at least one of said sub-patterns comprises a periodic array of bars and wherein each of said bars has a solid portion and a subdivided portion, the apparent position of each bar when observed being dependent on said performance parameter of the lithographic process.

18. A substrate as claimed in claim 14 , wherein said first and second sub-patterns have been formed in separate lithographic steps, and said performance parameter is overlay.

19. A substrate as claimed in claim 14 wherein said first and second sub-patterns extend side-by-side in a longitudinal direction of the pattern.

20. A substrate as claimed in claim 19 wherein a first one of said first and second sub-patterns extends along a centerline of the pattern, while the other one of said first and second sub-patterns extends along both sides such that the pattern as a whole is symmetric about said centerline.

Assignees

• Deckers David
• Bijnen Franciscus Godefridus Casper
• Musa Sami
• Asml Netherlands Bv

Inventors

• Deckers David
• Bijnen Franciscus Godefridus Casper
• Musa Sami

Classifications

• G03F7/70633

  Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching · CPC title

• G03F7/70683 Primary

  Mark designs · CPC title

• G03F9/7088

  Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection · CPC title

• G03F9/7076

  Mark details, e.g. phase grating mark, temporary mark · CPC title

• G03F1/70

  Adapting basic layout or design of masks to lithographic process requirements, e.g., second iteration correction of mask patterns for imaging · CPC title